Copper electroplating baths



United States Patent 3,023,152 CGPPER ELECTROPLATING BATHS Wennemar Strauss and Hans Wedell, Dusseldorf-Holthausen, Germany, assignors to Dehydag, Deutsche Hydrierwerke G.m.b.H., Dusseldorf, Germany, a corporation of Germany No Drawing. Filed Apr. 28, 1960, Ser. No. 25,242 Claims priority, application Germany May 6, 1959 22 Claims. (Cl. 204-52) The present invention relates to the production of level, full bright copper electro deposits from acid full bright copper electroplating baths, and it is particularly directed to the achievement of a good leveling efiect over a very wide current density range.

It is known that thiourea derivatives which contain one or more alkyl or aryl radicals in the molecule may be used as leveling agents in acid full bright copper electroplating baths. Particularly effective for this purpose have been found to be alkyl or aryl derivatives which contain hydroxyl and/ or ether groups in the alkyl and/or aryl radical. However, the effect of the above named compounds does not show itself over the entire technically interesting current density range.

it is an object of this invention to provide an electroplating process operable over a wide current density range from which level, bright copper deposits may be obtained.

It is a further object of this invention to provide a leveling agent for electroplating baths from which level copper electro deposits may be obtained.

it is another object to provide a leveling agent for copperplating baths which may be used over a wide current density range.

Yet another object is to provide leveling additives for copperplating baths which may be used in conjunction with full brightening agents, ductility agents and in direct acid copperplating baths, as Well as with other conventional additives.

These and other objects of our invention will become apparent as the description thereof proceeds.

We have now found that a considerable improvement can be achieved in acid full bright copper electroplating baths and the above objects achieved by using, along with the customary brightening chemicals, those alkyl and aryl derivatives of thiourea which contain at least one carboxyl group attached to an alkyl or aryl radical, in place of the above indicated thiourea derivatives. It has further been found that the alkyl and aryl radicals carrying the carboxyl group must be attached to the remainder of the molecule through a nitrogen atom because compounds in which these radicals are attached to the remainder of the molecule through the sulfur atom do not produce a leveling effect.

Such compounds have a general structural formula as follows:

R s R N i N R/ \R wherein R represents hydrogen, alkyl, aryl, carboxy-alkyl or carboxy-aryl radicals and at least one R radical is always a carboxy radical.

The superiority of the thiourea derivatives having carboxyl groups in the molecule in comparison to other leveling agents is particularly exhibited in the large current density tolerance of electroplating baths modified therewith; such baths are also fully etfective in low current density ranges. By concurrent use of these agents with known full brightening agents it is possible to achieve high quality copper electroplates which are completely level and which are mirror bright over the entire current densit I range.

' 2 Examples of suitable thiourea derivatives are the salts, especially the alkali metal salts, of the following carboxylic acids:

N-phenyl-N'-carboxymethylthiourea N-phenyl-N-carboXypentyl-thiourea N-phenyl-N-4-carboXyphenyl-thiourea N-plienyl-N-3-carboxyphenyl-thiourea N-phenyl-N-3,4 dicarboxyphenyl-thiourea N-butyl-N'-4-carboXyphenyl-thiourea N-octyl-N'3,4dicarboxyphenyl-thiourea N-butyl-N-carboxymethyl-thiourea N-rx-naphthyl-N-carboxymethyl-thiourea The thiourea derivatives according to the present in vention exhibit a good leveling effect primarily with those full brightening agents which contain one or more carbon atoms in the molecule, the carbon atoms being bonded only to hetero atoms, and which include a short aliphatic radical which is attached to the molecule through a sulfur atom, the aliphatic radical carrying a sulfonic acid group or another water solubilizing group. Examples of such full brightening agents are:

N,N-pentamethylene-dithiocarbamic acid-n-propylester-wsodium-sulfonate N,N-dimethyl-dithiocarbamic acid-n-propylester-w-sodium sulfonate N,N-diethylamino-dithiocarbamic acid S-propandiol-Zj N butyl dithiocarbamic acid N,S,-bis-propane-w-potassium-sulfonate Dithiocarbamic acid-S-methylester-N-ethy1-N-butyl-w-potassium sulfonate 1,3,5-triazine-2,4,6-trimercapto 2 hydroxy sodium-propionate 1,3,5 triazine-2,4,6-trimercaptoethane-ammonium sulfonate and other full brightening agents of similar structure as disclosed in United Stateslatent Nos. 2,849,351 and 2,849,352.

The concurrent use of the thiourea derivatives according to the invention with the above described full brightening agents may also be particularly applied to the process for direct copper electroplating, in which firmly adhering copper electroplates are applied to non-precious metals, such as iron, without preliminary copperplating in a cyanide bath; this method comprises subjecting the metal objects to be copperplated to a preliminary treatment in an acid pickling bath modified with inhibitors having a high inhibiting effect, and subsequently electroplating the pickled objects in an acid copper bath without an intermediate rinsing step.

In order to increase the ductility of the copper electroplates produced from the baths containing the above agents, it has further been found to be advantageous to add certain organic amino compounds which are free from carboxylic groups, such as 1,3-propylene-diamine, 1,3-bis-(diethylamino)-propanol 2,N,N,N,N-tetrabutyl- 1,3 diaminopropanol 2,N,N,N,N', tetraethyl 1,3-diarnino-propanol-Z or also their sulfuric acid or sulfonic acid ester derivatives which contain one or more sulfonic acid groups or sulfonic acid ester groups. Other suitable agents for increasing the ductility are halogen-containing tertiary amino compounds free from carboxyl groups, such as 2-diethylamino-3-chloropropano1-2, or the quaternary rearrangement products formed from these compounds which contain the halogen in ionogenic linkage. Such compounds are disclosed in United States application Serial No. 735,360 and Patent No. 2,842,488.

The thiourea alkylor aryl-carboxylic acids in accordance with the present invention or their salts are used in amounts from 0.0001 to 2.5 grams per liter of bath spasms fluid; otherwise, the baths are operated under the customary conditions of concentration and temperature. The process may be operated over a wide current density range of from 0.02-10 ampere per square decimeter.

The following specific examples are given to illustrate our invention and to enable persons skilled in the art to better understand and practice the invention and are not intended to be limitative.

Example I An acid copper bath which contained 2.0 gram per liter copper sulfate H 0, 60 grams per liter concentrated sulfuric acid and, as brightening agents, 0.05 gram per liter N,N-diethyl-dithiocarbamic acid-ethylester-wsodium sulfonate as well as 0.25 gram per liter N,N,N',N- tetrabutyl-l,S-diaminopropanOl-Z and 2.5 grams per liter of the reaction product of dodecyl alcohol and 8 mols ethyleneoxyd, was modified with 0.004 grams per liter of the sodium salt of N-phenyl-N'-carboxymethyl-thiourea. Full bright copper electroplates were obtained on unpolished brass plates within a current density range of 0.25 to 8 amperes per square decimeter. With the aid of this electroplating method, uneven spots of about 7 microns in depth were leveled with copper deposits of 15 to 20 microns in thickness. Without the addition of the thiourea derivative the copper electro deposits were full bright, but they were not level.

Example 11 An acid copper bath as described in Example I, which contained 0.007 gram per liter of the sodium salt of N- phenyl-N'-4-carboxyphenyl-thiourea as the leveling agent instead of the sodium salt of N-phenyl-N-carboxymethylthiourea of Example I, produced a similar brightening and leveling effect.

Example III An acid copper electroplating bath as described in Example I, which contained 0.003 gram per liter of the sodium salt of N-phenyl-N-3-carboxyphenyl-thiourea as the leveling agent, produced a similar brightening and leveling effect.

Example IV An acid copper electroplating bath as described in Example I, which contained 0.016 gram per liter of the sodium salt of N-phenyl-N-carboxypentyl-thiourea produced a similar brightening and leveling effect.

While we have set forth certain specific examples and preferred modes of practice of our invention, it will be understood that the invention is not limited thereto, and that various changes and modifications may be made in our invention without departing from the spirit of the disclosure or the scope of the appended claims.

We claim:

1. A process for producing a smooth, bright copper electroplate on a rough surface metal base from acidic copperplating baths containing a brightening agent which comprises adding to said bath as a smoothing agent a derivative of thiourea having a structural formula as follows:

wherein R R R and R are selected from the group consisting of hydrogen, alkyl, aryl, carboxy-alkyl and carboxyaryl radicals, at least one of R through R, being selected from the group consisting of carboxy-alkyl and carboxy-aryl radicals, said smoothing agent being added in sufiicient amount to effect said smoothing of the copper plate.

2. A process for producing a smooth, bright copper electroplate on a rough surface metal base from acidic copperplating baths containing a sulfonic acid brightening agent which comprises adding to said bath as a smoothing agent a derivative of thiourea having a structural formula as follows:

R1 S R3 wherein R R R and R are selected from the group consisting of hydrogen, alkyl, aryl, carboxy-alkyl and carboxy-aryl radicals, at least one of R through R, being selected from the group consisting of carboxy-alkyl and carboxy-aryl radicals, said smoothing agent being added in sumcient amount to effect said smoothing of the copper plate.

3. The process of claim 2 wherein, in addition, the baths contain ductility agents selected from the group consisting of amino-compounds free from carboxyl groups, and sulionic acid and sulfuric acid ester derivatives thereof.

4. The process of claim 2 wherein, in addition, the baths contain as ductility agents compounds selected from the group consisting of halogen-containing tertiary amino compounds free from carboxyl groups and quaternary rearrangement products thereof in which the halogen is present in ionogenic linkage.

5. The process of claim 2 wherein the thiourea derivative is the sodium salt of N-phenyl-N-carboxymethylthiourea.

6. The process of claim 2 wherein the thiourea derivative is N-phenyl-N-4-carboxyphenyl-thiourea.

7. The process of claim 2 wherein the thiourea den'vative is N-phenyl-N-3-carboxyphenyl-thiourea.

8. The process of claim 2 wherein the thiourea derivative is N-phenyl-N'-carboxypentyl-thiourea.

9. A process for producing a smooth, bright copper electroplate on a rough surface metal base from acidic copper plating baths containing a brightening agent having a carbon atom linked exclusively to heteroatoms, said carbon atom being further linked through a sulfur atom a, to a lower aliphatic chain which carries a water solubil- E S R i H a wherein R R R and R are selected from the group consisting of hydrogen, alkyl, aryl, carboxy-alkyl and carboxy-aryl radicals, at least one of R through R, being selected from the group consisting of carboxy-alkyl and carboxy-aryl radicals, said smoothing agent being added in sufiicient amount to effect said smoothing of the'copper plate.

10. The process of claim 9 wherein the water solubilizing radical is a sulfonic acid radical.

11. An electroplating bath for producing smooth, bright copper electrodeposits on rough surface metal bases comprising an aqueous solution of an inorganic salt of the copper to be electrodeposited, a brightening agent and as a smoothing agent a derivative of thiourea having a structural formula as follows:

R i R;

wherein R R R and R are selected from the group consisting of hydrogen, alkyl, aryl, carboxy-alkyl and carboxy-aryl radicals, at least one of R through R, being selected from the group consisting of carboxy-alkyl and carboXy-aryl radicals, said smoothing agent being present in sufficient amont to effect said smoothing of the electrodeposit.

12. An electroplating bath for producing smooth, bright copper electrodeposits on a rough surface metal base comprising an aqueous solution of an inorganic salt of the copper to be electrodeposited, a sulfonic acid brightening agent and as a smoothing agent a derivative of thiourea having a structural formula as follows:

NC-N Rg Ra wherein R R R and R are selected from the group consisting of hydrogen, alkyl, aryl, ca'rboxy-alkyl and carboxy-aryl radicals, at least one of R through R, being selected from the group consisting of carboxy-alkyl and carboxy-aryl radicals, said smoothing agent being present in suflicient amount to effect said smoothing of the electrodeposit.

13. The bath of claim 12 wherein, in addition, the baths contain ductility agents selected from the group consisting of amino-compounds free from carboxyl groups, and sulfonic acid and sulfuric acid ester derivatives thereof.

14. The bath of claim 12, wherein, in addition, the baths contain as ductility agents compounds selected from the group consisting of halogen-containing tertiary amino compounds free from carboxyl groups and quaternary rearrangement products thereof in which the halogen is present in ionogenic linkage.

15. The bath of claim 12 wherein the thiourea derivative is the sodium salt of N-phenyl-N'-carboxymethylthiourea.

16. The bath of claim 12 wherein the thiourea derivalive is N-phenyl-N-4-carboxyphenyl-thiourea.

17. The bath of claim 12 wherein the thiourea derivative is N-phenyl N-3-carboxyphenyl-thiourea.

18. The bath of claim 12 wherein the thiourea derivative is N-phenyl-N'-carboxypentyl-thiourea.

19. An electroplating bath for producing smooth,

bright copper electrodeposits on a rough surface metal base comprising an aqueous solution of an inorganic salt of the copper to be electrodeposited, a brightening agent having a carbon atom linked exclusively to heteroatoms, said carbon atom being further linked through a sulfur atom to a lower aliphatic chain which carries a water solubilizing radical, and as a smoothing agent a derivative of thiourea having a structural formula as follows:

wherein R R R and R are selected from the group consisting of hydrogen, alkyl, aryl, carboxy-alkyl and carboxy-a'ryl radicals, at least one of R through R; being selected from the group consisting of carboxy-alkyl and carboxy-aryl radicals, said smoothing agent being present in sufiicient amount to effect said smoothing of the electrodepoist.

20. The bath of claim 19 wherein the water solubilizing radical is a sulfonic acid radical.

21. The process of claim 2 wherein the amount of smoothing agent added is from about 0.0001 to about 2.5 g/ 1.

22. The bath of claim 12 wherein the amount of smoothing agent added is from about 0.0001 to about References Cited in the file of this patent UNITED STATES PATENTS 2,563,360 Phillips et a1. Aug. 7, 1951 2,696,467 Overcash et al Dec. 7, 1954 2,738,318 Fellows et al. Mar. 13, 1956 2,954,331 Abbott Sept. 27, 1960 

1. A PROCESS FOR PRODUCING A SMOOTH, BRIGHT COPPER ELECTROPLATE ON A ROUGH SURFACE METAL BASE FROM ACIDIC COPPERPLATING BATHS CONTAINING A BRIGHTENING AGENT WHICH COMPRISES ADDING TO SAID BATH AS A SMOOTHING AGENT A DERIVATIVE OF THIOUREA HAVING A STRUCTURAL FORMULA AS FOLLOWS: 